Origin of the near infrared luminescence in n-type Al_xGa_1-xAs alloys

A detailed analysis of the near-infrared luminescence has been performed in undoped and n-doped (Si, Te, Sn) AlGaAs samples grown by MBE and MOVPE techniques. A wide range of Al compositions (26-74%) and donor concentrations (10¹⁶-10¹⁸ cm^-3) was examined. In the spectral region from 0.9 to 2.0 mu m in all samples there is a photoluminescence (PL) peak at 1.1 mu m (IR1). MOVPE samples show an additional PL peak at 1.5 mu m (IR2), which is independent of the Al mole fraction, the doping concentration and the donor species IR2 is not present in MBE-grown samples, where a third peak IR3 appears. None of the IR peaks is related to DX deep donor centres, since the amplitudes of all IR peaks are independent of the donor doping level. By optically detected ESR of Si-doped samples it was shown that the IR2 band is due to arsenic antisite defects and not to DX centres as previously assumed. Also, deep level transient spectroscopy measurements were performed on Si-doped samples.